Fatigue life of SCS-6/timetal® 834 at room temperature and 600°C: Experiments and modeling

Fatigue of the titanium matrix composite (TMC) SCS6/Timetal 834 has been investigated at room temperature and 600°C. Whereas the room temperature behavior is mainly influenced by fatigue crack formation and growth, this is not the case for fatigue at 600°C. The runout specimens did not show any crack, whereas runout specimens tested at room temperature showed multiple transverse cracks with a characteristic distance. The main reason for the lack of cracks was found to be the result of stress relaxation of the matrix. This effect is strong due to the fact that the first 10⁵ cycles are performed at a low frequency (0.25 Hz). In the second part of this work attention is focused on modeling the most important damage mechanism under room temperature conditions. Initial computation of crack growth rates in TMC, assuming interfacial friction being the only stress transfer mechanism (i.e., bond strength is considered to be zero), proved to be unrealistically high. For that reason in the present work crack growth rates are calculated considering a fiber/matrix bond strength and friction in case the bond breaks. In this case three dimensional finite element models deliver more accurate crack growth rates.